This invention covers a pneumatically operated double acting piston and cylinder combination operating in a pressurized high temperature environment such as that which exists in a pressurized fluidized bed combustion boiler.
The pressurized fluidized bed combustion boiler is a unique steam generator which incorporates fluidized bed technology with gas turbine technology to effectively burn high sulphur coal while meeting current stringent environmental requirements. The pressurized fluidized bed combustion boiler process removes sulphur during combustion of the coal and because of the low bed and furnace temperatures, approximately 1,600.degree. F., the concentration of nitrogen oxides in the flue gases is extremely low compared to normal pulverized coal fired boiler emissions. Cleaned combustion gases from the process are used to drive a gas turbine which in turn drives an air compressor and an electric generator. For improved efficiency, the pressurized fluidized bed combustion boiler is located within a pressure vessel which operates at pressures between 50 and 250 psia as a function of boiler load. The air compressor associated with the gas turbine provides the means of pressurizing the vessel and also provides combustion air for the process. Because of the severe pressure and temperature conditions prevailing within the pressure vessel, actuators which provide the means for movement of internal mechanisms such as dampers, valves or other controls, are normally located outside the pressure vessel in ambient conditions while complex and elaborate sealing systems are required at pressure boundary penetrations for movable drive mechanisms associated with the actuators.
Double acting piston-cylinder combinations and associated valve arrangements are not new in the art. For example, U.S. Pat. No. 1,027,957 to W. H. Withers et al, discloses a piston-cylinder arrangement in which pressurized fluid is admitted to either side of piston 13 through the action of slide valve 29. U.S. Pat. No. 1,232,797 to T. A. Hedendahl discloses a fluid pressure controlled reversing gear which includes a double acting piston and cylinder combination controlled by a slide valve wherein a common source of fluid pressure provides the motive power. U.S. Pat. No. 3,441,100 to D. E. Stein discloses a pneumatic weight transmitter which operates in a controlled environment, either positive or negative pressure.